Absorbent paper product and process of producing the same



Patented Mar. 3, 1936 PATENT OFFICE ABSORBENT PAPER PRODUCT AND PROCESSOF PRODUCING THE SAME Merrill A. Youtz, Green Bay, Wia, asslgnor toNorthern Paper Mills, Green Bay, Wis.

No Drawing. Application August 18, 1933, Serial No. 685,786

1 Claim.

This invention relates to absorbent paper prodnets and processes ofproducing the same, and it comprises an absorbent paper such astoweling, absorbent type toilet paper, blotters, and similar highlyabsorbent materials derived from wood pulp, and in which have beenincorporated small amounts of added substances to preserve the paperagainst loss of absorbency; it further comprises processes wherein suchpreservatives are incorporated in the paper, for example by adding thesubstances to the beater, by spraying a solution of the preservative onthe wet sheet as it leaves the wire of the paper machine but before ithas been dried, or by spraying a solution of the preservative on thedried paper and again i y s.

Paper toweling, absorbent type toilet papers, blotters and other paperproducts primarily used to" a sorb moisture differ from bond, writing,printing, and other substantially non-absorbent, or, at themost,superficially absorbent, paper. These differences are found in part inthe actual manufacturing steps employed and also in the manner ofcooking the pulp. Since absorbent papers must take up water rapidly, thebeating and jordanning of the pulp are comparatively slight so that thepulp will not become to gelatinous and too much cut up. If the beatingis prolonged, as for example in making bond paper, the resulting sheetis hard and the fibers are so closely associated as to preclude theuseof such a felted sheet for paper toweling. In the manu-' facture ofabsorbent papers it is also desirable that the formation or structuralrelation of the fibers be as uneven and wild as possible, consistentwith some strength, so as to increase both the rate of absorption andthe absorptive capacity of the paper. Toweling is generally creped orembossed to further soften and break up fiber formation and thusincrease absorption. The pulp is also somewhat more severely cooked thanpulp used for making non-absorbent types of paper. This is to soften itand. open up passages and holes in the fiber. It also thoroughly removesincrusting substances such as lignin and rosin, both of which tend tomake the paper hard and less absorbent.

These difierences in manufacturing operations are reflected in thephysical properties of the paper. Paper toweling and blotters, forexample, are unsized, and have surfaces which are highly porous andsoft. Parchment, bond, writing,

printing, and wrapping papers are relatively hard surfaced, lack markedporosity, and are filled and sized.

Present absorbent papers show greatly lessened absorbency afterprolonged storage prior to use. One of the paper towels I have testedfor absorbency lost as much as one-half of its ability to absorb waterafter six months storage. Another toweling showed a ninety percent lossin absorbency. Just why absorbent paper loses its initial high capacityfor absorbing water is not entirely clear. I have, however, found thatthe loss bears no relation to changes in the strength, moisture,content, softness and flexibility of the paper. These qualitiesgenerally remain substantially the same during aging in storage althoughthe paper may have lost from fifty to ninety percent of its capacity forabsorbing water. My investigations have suggested that beta and gammacelluloses are involved in the matter. It is probable that thesecelluloses more or less generally form a coating on the fiber comprisingthe paper and that, on storage, these celluloses lose water bytransference thereof to the alpha cellulose fiber in the paper. Loss ofwater converts the beta and gamma cellulose to a hard, dried, gelcondition and, after such conversion, these forms of cellulose are notreadily wetted again. The change is irreversible, in other words, lossof water from the beta and gamma celluloses converts them toirreversible gel form. That this is a rea sonable explanation for theloss in absorbency is shown by the fact that paper which is very high inalpha cellulose does not develop the phenomenon of absorbency loss onstorage. This is because a high alpha cellulose paper is substantiallyfree of those beta and gamma celluloses which pass-irreversibly to ahard, dried gel condition.

In order to determine the loss of absorbency on storage rapidly, andalso to determine the effectiveness of the many preservatives againstsuch loss which I shall hereinafter disclose, I can make use of a quickaging test. This consists in heating the paper in an oven at C. for onehour. Absorbency is determined. both before and after such acceleratedaging, and this absorbency is measured by the time in seconds required.for the paper to absorb one cubic centimeter of water. Paper towelingmay also be tested for absorbency by determining its absorbency whenfreshly made, storing it for six months and then testing it again forabsorbency.

For example, the following table illustrates the very greatdeterioration, or loss of absorbency, in ordinary bleached andunbleached paper toweli'ng over six months.

When making comparisons papers it is best to use the ratios ofabsorbency before and after storage as shown in the third column in theabove tables.

The accelerated aging test described above is about equivalentto sixmonths storage.

I have determined that this phenomenonof loss of absorbency is not dueto oxidation. The loss develops even when the paper is subjected toaccelerated aging in an atmosphere of pure nitrogen. The loss is alsonot due to a mere drying out of the paper, that is, removal of freemoisture, for variations in the amount of freemoisture due to partialdrying out do not affect absorbency. Freshly made paper usually containsabout 6 to 9 percent of free moisture.

It will thus be apparent that obscure reactions, some chemical, andothers of a morephysical nature, perhaps involving colloidal chemicalphenomena, take place in the paper during storage. I have oiiered onereasonable explanation for the changes noted experimentally, but I donot, of course, wish to be bound by the theory presented above. I

In the present invention, I have had for my object the discovery of someway of preventing this loss in absorbency; in other words I haveendeavored to find ways of preserving all. or at least a large part ofthe normal capacity of freshly made paper for absorbing water.

I have now discovered that the addition of very small amounts of certainsubstances to the paper will inhibit loss of absorbency. This is, ofcourse, in a sense a preservative action, but in the case of manysubstances I believe that the action is a sort of negative catalysissince it prevents what I believe to be a normal transference of waterfrom beta and gamma cellulose to the alpha cellulose in the paper.

I have found that one of the very best groups of such preservativesubstances to add to the paper for this purpose are compounds commonlyreferred to as wetting agents. These are generally sulfonated andsulfated organic compounds.

Many of them go under trade names. A common one is Turkey red 011.Another is sulfonated neats foot oil. In most instances the addition ofas little as 0.2 percent, based on the weight of the paper, prevents allloss of absorbency over a period of six months or more. Such substances,when incorporated in the paper, produce no apparent change in itsoutward properties. Stiffness, softbetween various ness, color,flexibility and tensile strength remain the same, although the lattermay be reduced very slightly but cannot be detected except by the use ofvery accurate instruments. Occasionally the addition of the preservativemay increase the absorbency somewhat. If the added substance be quiteoily, it may soften the paper slightly and reduce. its "rattle" but allof these changes are slight and inconsequential since I add such smallquantities of wetting agents to the paper. My added substances functionprimarily to prevent loss of absorbency. They have little or no effecton any other properties of the paper.

Those substances which show the bestpreserv- 'ative action, that is, thesulfonated and sulfated to be effective, but which do not function inthe same way as-the wetting agents, are normally liquid polyhydricalcohols such as glycerine, glycol, and ethanolamine. These substancesare hygroscopic. Greater quantities, of the order of 2 percent arenecessary and this indicates a difference in the way the two groups act.I do not believe that these hygroscopic substances function merely byholding water in the absorbent paper, or by keeping it slightly moist.They may incidentally do this but I believe that they function chieflyby coating the fibers, thus retaining water in the beta and gammacelluloses. But this has nothing to do with the actual amount ofuncombined water in the paper.

In addition to sulfonated oils and polyhydric alcohols, I have alsofound that certain alkalinereacting inorganic salts such as borax, sodaash, and sodium sulfite will act as preservatives. This action appearsto be quite specific. Neutral or acid salts show no preservative action,in fact they actually increase loss of absorbency. It is possible thatthe alkaline salt neutralizes any actual or potential acidity in thepaper. 'This acidity, were it allowed to progress, would degrade thecellulose locally into beta and gamma cellulose and the latter wouldthen lose water to form irreversible gels.

Of these three classes of compounds I find that the wetting agents arethe best. The effectiveness of any particular preservative, or that of asubstance thought to have preservative properties, can, however, bedetermined readily either by the accelerated aging test given above orby permitting the treated paper to age normally for six months or more.i

The preservative can be incorporated in the paper in various ways.Perhaps the easiest way to test the effectiveness of any particularagent is to simply dipthe towel or other absorbent paper in a diluteaqueous solution of-the preservative and then allow the wet paper to dryin air. Hereinafter I shall describe various commercial methods ofincorporating the preservative in the paper.

The following tables will illustrate the effectiveness of differentwetting agents applied by dipping the paper toweling in a dilute aqueoussolution of the preservative and allowing the towel to dry in air. Ineach instance, the dried,

heated towel contained 0.2 percent of preservative.

Bleached towels tit;

absorbency Treated-Substance :33 32 tvglien made added m mam six months1 to 3.4 Nee 1 to 1.12 1 to 3.4 Neomcrpin SA. oono- 1 to 1.04 1 to 3.4N. S. L. neutral. 1 to 1.56 1 to 2.88 N. S. L. acid. 1 to 1.62 1 to 1.511 to 1.0 1 to 3.4 1 to 1.08 1 to 2.66 ardinol 1 to 1.0 1 to 3.4 Greenacid soap, 11-1743. 1 to 1.32

Unbleached towels Untreated Treated l to 1.0 Neopen l to 1.21 1 to 1.9Neomerpin SA. cono 1 to 1.05 1 to 1.9 N. S. L. neutraL.-. 1' to 1.41 1to 1.9 N. B. L. acid 1 to 1.3 1 to 1.32 Ne 1 to 1.1 l to 1.4 Permeko 1to 1.03 1 to 1.48 Gar ol..-. 1 to 1.0 1 to 1.0 Green acid soap Ll743 1to 1.44 1 to 3.61 Turkey red oil 1 to 1.06 1 to 3.61 811110. neats-iootoil.-- 1 to 1.36 H

It will thus be noted that the addition of as little as 0.2 percent ofNekal to the toweling practically completely prevents loss of absorbencyover a period of six months. The same paper unprotected would lose aboutfifty percent of its ability to absorb water.

About the same figures are obtained when Gardinol isused. As statedabove, most of these wetting agents so by trade names. They are allsulfonated oils of various-types and I usually use them in the form oftheir sodium or ammonium salts. Neopen is the trade name of a materialproduced by dry distilling rosin, treating the distillate with fumingsulfuric acid, and converting the sulfonic acid thus obtained to itssodium salt. Nekal and Neomerpin are the sodium salts of alkylatednaphthalene sulfonic acid. Usually the alkyl group is isopropyl.Gardinol and Ocenol are the sodium or ammonium salts of alkyl sulfatesof aliphatic alcohols of rather high molecular weight. In general thesesubstances are all alkali metal salts of aliphatic or aromatic sulfonicacids or the alkali alkyl sulfates.

Sometimes soap is referred to as a wetting agen but this is in fact amisnomer. The term has a fairly restricted and definite meaning in theart and excludes common soap and other sodium salts of the siniplehigher fatty acids. As a matter of fact, soap is entirely unsuitable andincreases loss of absorbency. One paper towel had, before treatment withsoap, an absorbency ratio of 1 to 3.61. After incorporating 0.65 percentof soap and aging the absorbency ratio was 1 to 7.07.

I find that the manner in which the wetting agent is incorporated in thepaper does not have very mucheifect on the preservative action. However,it has been found in the case of Neopen, one of the best to use, smalleramounts are required if a dilute solution of the agent is sprayed on thetowel while the wet web is leaving the wire of the paper machinebutbefore drying. Thus, as little, as 0.05 percent of Neopen retained inthe towel is suflicient to prevent aging to a satisfactory degree.

I have stated above that the normally liquid polyhydric alcohols arealso eflective. In the following table I have illustrated the results oftests on various alcohols of this class.

Bleached towels Ratio gg gfi Alcohol Percent treatment treatment 1 to3.4 Ethylene glycol.-. 3 1 to 2 72 1 to 3.4 Diethylene glycol. 2 1 to 248 1 to 3.4 Triethylenc g ycoL-. 2 1 to 1 8 1 to 3.4 Triethano 2 1 to 143 1 to 3.4 Glycerine l0 1 to 1 21 Unbleached towels 1 to 1.94 Ethyleneglycol"... 2 1 to 1.34 1 to 1.94 Diethylene $1 001... 2 l to 1.45 1 to1.94 Triethylene g 001... 2 1 to 1.40 1 to 1.94 Triethanolemine.--. 2 1to 1.63 1 to 1.04 Glycerine 10 1 to 1.79

But it will be noted that these substances are not as satisfactory formost purposes as the wetting agents.

The following table illustrates the effectiveness of variousalkaline-reacting salts, the paper containing 2 percent.

Bleached towels Absorbency Absorbency ratio beiore Substance ratio aftertreatment treatment 1 to 3.4 NmHPO 1 to 2.82 1 to 3.4 Born: 1 to 2.08 lto 3.4 N11100: 1 to 2.09 1 to 2.86 Nelson 1 to 2.34

Unbleached towels 1 to 2.6 NaaHPO. 1 to 1.43 1 to 1.94 Borax 1 to 1.68 1to 1.04 NW0: 1 to 1.15 l. to 1.94 N8|S0| 1 to 1.23

0n the other hand, substances like aluminum sulfate, sodium sulfate andcommon salt actually increase loss of absorbency. The first two nearlydouble the loss and the sodium chlorid triples it.

If desired, two or more preservatives can of course be added to thepaper. Usually only one is sufflcient but in the interests of economy Isometimes find it advantageous to add a small amount of a more expensivepreservative and augment its effect by including another less expensiveagent.

When practising my invention commercially, I generally find it mostadvantageous to incorporate the preservative in the paper by simplyspraying an aqueous solution of the preservative on the wet web of pulpafter it leaves the wire of the paper machine but before drying.Alternatively, I can add the preservative, or a mixture thereof, to theheater and make the paper from the beaten pulp in the usual way, or theaqueous solution can be sprayed on freshly made dried paper and thepaper re-drled. This is better than dipping the paper in an aqueoussolution of the preservative but the dipping method can be practised.Other suitable ways can of course be employed. When using the wettingagents, I find it advantageous to spray the wet pulp with an aqueoussolution usually containing up to about percent of the agent. The exactconcentration depends upon the amount of water which can be convenientlysprayed and the amount oi! preservative to be applied. Generally asolution containing to 1 or 2 percent of the preservative is best. Anyalum in the paper, or added thereafter assists in fixing thepreservative in the body of the'paper. It should be noted that thisinvention bears no similarity to the-common addition of glycerine andglycol to ordinary non-absorbent papers. It

is of course an old proposition to incorporate various amounts ofhygroscopic polyhydric alcohols in printing and wrapping papers,vegetable parchment, and like hard-surfaced substantially nonporousproducts. This, however, is simply to keep the paper soft by preventinga physical drying out or the paper. It has nothing to do with the actualability of the paper to absorb large quantitles of water.

, Similarly it is old to add small quantities of various alkalis topaper such as newsprint and it has even been suggested to incorporateTurkey red'oil and naphthalene sulfonic acids to control the ability ofprinting papers to absorb coloring agents. In this case the addedmaterial is simply used as an ordinary wetting agent to promoteabsorption in a paper which is not readily absorbent for water. This isa common procedure when it is desired to color the paper with aqueoussolutions of various dyes, etc.

But none of these prior processes deal with highly absorbent, unsizedand usually unfilled papers and none of them are concerned withpreventing loss of absorbency in such products.

Throughout this specification, and in the appended claim. I have usedthe words highly absci-bent paper" to denote paper products like papertoweling, absorbent type toilet paper, blotters and the like. I do notmean this language to include writing, bond, newsprint, wrapping, andlike papers which are but very slightly absorbent, or superficiallyabsorbent to a degree Just suflicient to permit them to take up ink.

And by the term sulionated organic material classed as a wetting agent,I mean to include sulphonic acids, alkyl sulphuric acids, and theirwater soluble salts such as the sodium and ammonium salts. I do notintend that this terminology shall include such substances as commonsoap.

Having thus described my invention, what I claim is:

The method of decreasing the normal loss of absorbency in unsizedabsorbent paper toweling when such toweling is stored for periods of sixmonths or longer which consists in incorporating in the freshly-madetoweling prior to storage thereof a small amount, of the order of .05 to0.2 percent, based on the weight of the paper, of an organic materialclassed as a wetting agent and being chosen from the group consisting ofsulfated and sultonated oils, sulfonated rosin distillates. alkylsuliates of higher alcohols, alkylated naphthalene sulfonic acids, andsalts of these substances, said salts also being wetting agents, saidpaper towel containing the wetting agent displaying substantially noincrease in absorbency when compared with papertowellng from the samestock but which does not contain said wetting agent.

MERRIEL A. YOUTZ.

